1. Field of the Invention
The present invention relates to polymer-modified polyol dispersions and to processes for production thereof, and use thereof to produce polyurethane foams. More particularly, the present invention relates to polymer-modified polyol dispersions having a combination of high solids content and improved stability.
2. Description of the Prior Art
Polymer-modified polyol dispersions are known and, in the context of dispersions used to make polyurethane foam, are often referred to as PIPA (PolyIsocyanate PolyAddition) polyols. These terms will be used interchangeably throughout this specification.
A useful background discussion on PIPA polyols may be found in "PIPA-Process For The Future"; Picken, K., Urethanes Technology, June 1984, pg. 23-24, the contents of which are incorporated herein by reference. PIPA polyol is a dispersion in which the polyol acts as a substantially inert carrier for PIPA particles. The PIPA particles are formed by the reaction of an isocyanate and a trifunctional alkanolamine, optionally in the presence of an organotin catalyst. The reaction product is an array of alkanolamine and isocyanate groups having pendant hydroxyl groups for further reaction.
One of the earliest patents relating to the production of PIPA polyols is U.S. Pat. No. 4,374,209 (Rowlands), the contents of which are incorporated herein by reference. Rowlands discloses the production of PIPA polyols by polymerizing an olamine with an organic polyisocyanate in the presence of a polyol. The olamine is described as an organic compound having one or more hydroxyl groups and also one or more amine groups. The olamine reacts at least predominantly polyfunctionally with the isocyanate. The polyol functions as a substantially inert carrier for the PIPA product. Rowlands purports to be able to produce a PIPA polyol having a solids content of from 1% to 35% by weight based on the weight of the polyol. It is noteworthy that Rowlands exemplifies PIPA polyols having a solids content of up to 20% by weight with the product at upper limit described as having "an acceptable viscosity".
U.S. Pat. No. 4,293,470 (Cuscurida), the contents of which are incorporated herein by reference, discloses a polyurea polyol with purportedly improved storage stability. Specifically, the subject polyurea polyol is produced by reacting a hydroxyl-containing amine, a polyether polyol and an organic polyisocyanate. The reaction product is then quenched with a secondary amine. In the Examples provided in Cuscurida, quenching of the reaction product was effected two to three hours after initiation of the reaction. U.S. Pat. No. 4,452,923 (Carroll et al.), the contents of which are incorporated herein by reference, discloses polymer-modified polyols. Specifically, there is disclosed a high strength polymer-modified polyol comprising a polyol and from about 40% to about 80% by weight of the reaction product of a polyisocyanate and a tertiary-N-polyolanine, based on the combined weight of the polyol and the reaction product. The tertiary-N-polyol is described as an organic compound having two or more hydroxyl groups and one or more tertiary amine groups. The use of a catalyst in the reaction is optional. It is apparent from the Examples that the proportion of the polyisocyanate and polyolamine in the reaction is important for achieving the purported advantages of the invention. Specifically, it is disclosed that the reaction is conducted such that the ratio of isocyanate groups to hydroxyl groups provided by the polyolamine is from 0.33:1 to 1:1. Indeed, Example 1 illustrates the importance of observing this ratio to avoid production of a low strength polyol (solids content of 10% by weight). It is also noteworthy that, beyond providing an indication of solids content, the high strength polyol is not isolated for complete analysis nor is there any indication provided of its viscosity. Indeed, one of the deficiencies of Carroll et al, is that the high strength polymer-modified polyol must be diluted immediately after production to prevent gelling thereof.
Heretofore, prior art PIPA polyols have suffered from being relatively unstable, notwithstanding the fact that much of this prior art purports to provide a polyol having a relatively high solids content (e.g. 25% or higher). The problem stems from the fact that it is very difficult to produce such a high solids content polyol which does not have to be diluted immediately after production to prevent gelling thereof. Indeed, to the inventors' knowledge, there is currently no commercially available polymer-modified polyol having a high solids content (e.g. greater than 20% by weight solids).
In light of the foregoing it would be desirable to have a polymer-modified polyol dispersion having a high solids content, a viscosity substantially below the gelling point and post-production stability as a function of little or no increase in the viscosity of the polyol dispersion. Numerous advantages would accrue from the provision of such a polymer-modified polyol dispersion. The major advantage would be that the high solids polymer-modified polyol dispersion could be produced in one site and safely shipped to the user at another site without dilution. This would result in an enormous savings in shipping costs since a larger volume of solids could be shipped at one time.